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systemd.mount - Mount unit configuration
A unit configuration file whose name ends in ".mount" encodes information about a file system mount point controlled and supervised by systemd. This man page lists the configuration options specific to this unit type. See systemd.unit(5) for the common options of all unit configuration files. The common configuration items are configured in the generic [Unit] and [Install] sections. The mount specific configuration options are configured in the [Mount] section. Additional options are listed in systemd.exec(5), which define the execution environment the mount(8) binary is executed in, and in systemd.kill(5), which define the way the processes are terminated, and in systemd.resource-control(5), which configure resource control settings for the processes of the service. Note that the User= and Group= options are not particularly useful for mount units specifying a "Type=" option or using configuration not specified in /etc/fstab; mount(8) will refuse options that are not listed in /etc/fstab if it is not run as UID 0. Mount units must be named after the mount point directories they control. Example: the mount point /home/lennart must be configured in a unit file home-lennart.mount. For details about the escaping logic used to convert a file system path to a unit name, see systemd.unit(5). Note that mount units cannot be templated. Optionally, a mount unit may be accompanied by an automount unit, to allow on-demand or parallelized mounting. See systemd.automount(5). Mount points created at runtime (independently of unit files or /etc/fstab) will be monitored by systemd and appear like any other mount unit in systemd. See /proc/self/mountinfo description in proc(5). Some file systems have special semantics as API file systems for kernel-to-userspace and userspace-to-userspace interfaces. Some of them may not be changed via mount units, and cannot be disabled. For a longer discussion see API File Systems.
If a mount unit is beneath another mount unit in the file system hierarchy, both a requirement dependency and an ordering dependency between both units are created automatically. Block device backed file systems automatically gain BindsTo= and After= type dependencies on the device unit encapsulating the block device (see below). If traditional file system quota is enabled for a mount unit, automatic Wants= and Before= dependencies on systemd-quotacheck.service and quotaon.service are added. For mount units with DefaultDependencies=yes (the default) a couple additional dependencies are added. Mount units referring to local file systems automatically gain an After= dependency on local-fs-pre.target. Network mount units automatically acquire After= dependencies on remote-fs-pre.target, network.target and network-online.target. Towards the latter a Wants= unit is added as well. Mount units referring to local and network file systems are distinguished by their file system type specification. In some cases this is not sufficient (for example network block device based mounts, such as iSCSI), in which case _netdev may be added to the mount option string of the unit, which forces systemd to consider the mount unit a network mount. Mount units (regardless if local or network) also acquire automatic Before= and Conflicts= on umount.target in order to be stopped during shutdown. Additional implicit dependencies may be added as result of execution and resource control parameters as documented in systemd.exec(5) and systemd.resource-control(5).
Mount units may either be configured via unit files, or via /etc/fstab (see fstab(5) for details). Mounts listed in /etc/fstab will be converted into native units dynamically at boot and when the configuration of the system manager is reloaded. In general, configuring mount points through /etc/fstab is the preferred approach. See systemd-fstab-generator(8) for details about the conversion. When reading /etc/fstab a few special mount options are understood by systemd which influence how dependencies are created for mount points. systemd will create a dependency of type Wants= or Requires (see option nofail below), from either local-fs.target or remote-fs.target, depending whether the file system is local or remote. x-systemd.requires= Configures a Requires= and an After= dependency between the created mount unit and another systemd unit, such as a device or mount unit. The argument should be a unit name, or an absolute path to a device node or mount point. This option may be specified more than once. This option is particularly useful for mount point declarations that need an additional device to be around (such as an external journal device for journal file systems) or an additional mount to be in place (such as an overlay file system that merges multiple mount points). See After= and Requires= in systemd.unit(5) for details. x-systemd.requires-mounts-for= Configures a RequiresMountsFor= dependency between the created mount unit and other mount units. The argument must be an absolute path. This option may be specified more than once. See RequiresMountsFor= in systemd.unit(5) for details. x-systemd.automount An automount unit will be created for the file system. See systemd.automount(5) for details. x-systemd.idle-timeout= Configures the idle timeout of the automount unit. See TimeoutIdleSec= in systemd.automount(5) for details. x-systemd.device-timeout= Configure how long systemd should wait for a device to show up before giving up on an entry from /etc/fstab. Specify a time in seconds or explicitly append a unit such as "s", "min", "h", "ms". Note that this option can only be used in /etc/fstab, and will be ignored when part of the Options= setting in a unit file. noauto, auto With noauto, this mount will not be added as a dependency for local-fs.target or remote-fs.target. This means that it will not be mounted automatically during boot, unless it is pulled in by some other unit. The auto option has the opposite meaning and is the default. nofail With nofail, this mount will be only wanted, not required, by local-fs.target or remote-fs.target. This means that the boot will continue even if this mount point is not mounted successfully. x-initrd.mount An additional filesystem to be mounted in the initramfs. See initrd-fs.target description in systemd.special(7). If a mount point is configured in both /etc/fstab and a unit file that is stored below /usr, the former will take precedence. If the unit file is stored below /etc, it will take precedence. This means: native unit files take precedence over traditional configuration files, but this is superseded by the rule that configuration in /etc will always take precedence over configuration in /usr.
Mount files must include a [Mount] section, which carries information about the file system mount points it supervises. A number of options that may be used in this section are shared with other unit types. These options are documented in systemd.exec(5) and systemd.kill(5). The options specific to the [Mount] section of mount units are the following: What= Takes an absolute path of a device node, file or other resource to mount. See mount(8) for details. If this refers to a device node, a dependency on the respective device unit is automatically created. (See systemd.device(5) for more information.) This option is mandatory. Where= Takes an absolute path of a directory of the mount point. If the mount point does not exist at the time of mounting, it is created. This string must be reflected in the unit filename. (See above.) This option is mandatory. Type= Takes a string for the file system type. See mount(8) for details. This setting is optional. Options= Mount options to use when mounting. This takes a comma-separated list of options. This setting is optional. SloppyOptions= Takes a boolean argument. If true, parsing of the options specified in Options= is relaxed, and unknown mount options are tolerated. This corresponds with mount(8)'s -s switch. Defaults to off. DirectoryMode= Directories of mount points (and any parent directories) are automatically created if needed. This option specifies the file system access mode used when creating these directories. Takes an access mode in octal notation. Defaults to 0755. TimeoutSec= Configures the time to wait for the mount command to finish. If a command does not exit within the configured time, the mount will be considered failed and be shut down again. All commands still running will be terminated forcibly via SIGTERM, and after another delay of this time with SIGKILL. (See KillMode= in systemd.kill(5).) Takes a unit-less value in seconds, or a time span value such as "5min 20s". Pass 0 to disable the timeout logic. The default value is set from the manager configuration file's DefaultTimeoutStart= variable. Check systemd.exec(5) and systemd.kill(5) for more settings.
systemd(1), systemctl(1), systemd.unit(5), systemd.exec(5), systemd.kill(5), systemd.resource-control(5), systemd.service(5), systemd.device(5), proc(5), mount(8), systemd-fstab-generator(8), systemd.directives(7)
1. API File Systems http://www.freedesktop.org/wiki/Software/systemd/APIFileSystems